Interactive input system and method

ABSTRACT

A method for human-machine interaction includes monitoring a movement of an object by a sensor that detects positions of the object over time, generating a time-dependent velocity of the object based on the movement of the object, detecting a tapping event of the object tapping on a surface by detecting a sudden change of the time-dependent velocity, and determining a position of the object at a time when the tapping event occurs as a tapping position of the object.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional applicationSer. No. 14/034,286 filed on Sep. 23, 2013, which is based upon andclaims the benefit of priority from U.S. Provisional Application No.61/811,680, filed on Apr. 12, 2013 and U.S. Provisional Application No.61/841,864, filed on Jul. 1, 2013. The entire contents of all of theabove-referenced applications are incorporated herein by reference.

TECHNOLOGY FIELD

The disclosure relates to input systems and methods and, moreparticularly, to input systems and methods based on detection ofthree-dimensional (3D) motion of a 3D object.

BACKGROUND

A computer user often needs to interact with the computer, which may berealized using an interactive input device, such as a keyboard, a mouse,or a touch screen. However, there are limits in using these devices. Forexample, conventional touch screens usually are based on technologiessuch as, for example, capacitive sensing or electric-field sensing. Suchtechnologies can only track objects, such as the user's fingers, nearthe screen (that is, a short operational range), and cannot recognizethe objects' 3D structure. Moreover, touch screens are usually used insmall computers such as table computers. For a larger computer, such asa desktop or a workstation, it is often not convenient for the user toreach to the screen.

Therefore, there is a need for a human-computer interactive input systemthat has a larger operational range, is accurate and fast to resolvefine objects, such as a user's fingers, and has the ability to track anobject's 3D motion and interaction with a surface.

SUMMARY

In accordance with the disclosure, there is provided a method forhuman-machine interaction. The method includes monitoring a movement ofan object by a sensor that detects positions of the object over time,generating a time-dependent velocity of the object based on the movementof the object, detecting a tapping event of the object tapping on asurface by detecting a sudden change of the time-dependent velocity, anddetermining a position of the object at a time when the tapping eventoccurs as a tapping position of the object.

Also in accordance with the disclosure, there is provided an apparatusfor human-machine interaction. The apparatus includes a sensing deviceconfigured to monitor a movement of an object by detecting positions ofthe object over time and a processor. The processor is configured togenerate a time-dependent velocity of the object based on the movementof the object, detect a tapping event of the object tapping on a surfaceby detecting a sudden change of the time-dependent velocity, anddetermine a position of the object at a time when the tapping eventoccurs as a tapping position of the object.

Further in accordance with the disclosure, there is provided a methodfor human-machine interaction. The method includes monitoring a movementof an object by detecting positions of the object over time. Eachposition of the object is detected by obtaining a two-dimensional (2D)image of the object taken from a viewing angle, extracting a 2D skeletonof the object from the 2D image, calculating a 3D skeleton of the objectbased on the 2D skeleton, and determining the position of the objectbased on the 3D skeleton of the object. The 2D skeleton includes a 2Dskeleton line representing a section of the object and the 3D skeletonincludes a 3D skeleton line representing the object. The method furtherincludes detecting a tapping event of the object tapping on a surface bydetecting a sudden change of the time-dependent velocity and determininga position of the object at a time when the tapping event occurs as atapping position of the object.

Features and advantages consistent with the disclosure will be set forthin part in the description which follows, and in part will be obviousfrom the description, or may be learned by practice of the disclosure.Such features and advantages will be realized and attained by means ofthe elements and combinations particularly pointed out in the appendedclaims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and together with the description, serve to explain theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows an interactive system according to anexemplary embodiment.

FIG. 2 is a flow chart showing a process according to an exemplaryembodiment.

FIGS. 3A and 3B schematically show a sensing device according to anexemplary embodiment.

FIGS. 4A-4C schematically show a sensing device according to anexemplary embodiment.

FIG. 5 schematically shows a sensing device according to an exemplaryembodiment.

FIGS. 6A and 6B schematically show the connection of sensing units to acomputer according to an exemplary embodiment.

FIGS. 7A and 7B schematically show exemplary arrangements of sensingunits relative to a display.

FIGS. 8A and 8B schematically show background surface coating accordingto exemplary embodiments.

FIG. 9 schematically shows a sensing device according to an exemplaryembodiment.

FIGS. 10A and 10B show a background surface with markers viewed by animaging sensor and by a naked human eye, respectively.

FIGS. 11A and 11B show patterns printed using different types of inksfor creating a background surface with markers according to an exemplaryembodiment.

FIG. 12 is a high level process flow schematically showing a sensingprocess according to an exemplary embodiment.

FIG. 13 shows an process for adjusting illumination sources and imagingsensors, and estimating a background according to an exemplaryembodiment.

FIG. 14 schematically shows a process for analyzing and recording abackground model according to an exemplary embodiment.

FIG. 15 schematically shows a process for recognizing and tracking aforeground object based on multiple imaging sensors according to anexemplary embodiment.

FIG. 16 schematically shows a process for finding a foreground objectand recognizing the foreground object's 2D structure for each imagingsensor according to an exemplary embodiment.

FIG. 17 shows an exemplary background model image.

FIG. 18 shows an exemplary input image captured during a hand trackingprocess.

FIG. 19 shows an exemplary foreground region.

FIG. 20 shows an exemplary result of probability calculation accordingto an exemplary embodiment.

FIG. 21 shows a result of the segmentation according to an exemplaryembodiment.

FIG. 22 schematically shows 2D boundaries of sub-parts of a hand.

FIG. 23 schematically shows center lines for fingers.

FIG. 24 schematically shows a finger tip.

FIG. 25 is a high-level flow chart showing a process for calculating 3Dinformation of a foreground object and sub-parts of the foregroundobject according to an exemplary embodiment.

FIG. 26 shows an association between fingers according to an exemplaryembodiment.

FIG. 27 shows an example of associating two skeleton lines.

FIG. 28 shows a 3D skeleton obtained according to an exemplaryembodiment.

FIG. 29 shows a calculation of a 3D boundary of a palm based on 2Dboundaries of the palm in two 2D images taken by two different imagingsensors.

FIG. 30 shows an exemplary output of hand skeleton calculation.

FIG. 31 schematically shows a 3D center of a palm calculated accordingto an exemplary embodiment.

FIG. 32 shows a model based framework.

FIGS. 33A and 33B schematically show exemplary setups of a systemaccording to exemplary embodiments and different types of touchinteractive surfaces.

FIG. 34 is a high-level flow chart showing a process for enabling a 2.5Dtouch interaction according to an exemplary embodiment.

FIG. 35 is a high-level flow chart showing a process for manuallycalibrating a touch interactive surface according to an exemplaryembodiment.

FIG. 36 shows a process for defining an effective interaction areaaccording to an exemplary embodiment.

FIG. 37 shows a result of defining corner points of a touch interactivesurface according to an exemplary embodiment.

FIGS. 38A and 38B show a finger's 3D velocity when the finger is movingin the air and when the finger hits a solid surface, respectively.

FIG. 39 is a flow chart showing a process for automatically detecting atouch interactive surface by detecting markers according to an exemplaryembodiment.

FIG. 40 is a flow chart showing a process for automatically detectingand calibrating a display screen according to an exemplary embodiment.

FIG. 41 schematically shows a 2D code shown on a display screen.

FIG. 42 is a flow chart showing a process for defining a virtual touchsurface according to an exemplary embodiment.

FIG. 43 schematically shows corner points of a desired virtual touchsurface.

FIG. 44 is a flow chart showing a process for converting 3D informationof a foreground object to 2.5D information according to an exemplaryembodiment.

FIG. 45 is a flow chart showing a process for determining the distance dbetween a foreground object and a touch interactive surface.

FIG. 46 is a flow chart showing a process for finding z′ according to anexemplary embodiment.

FIG. 47 is a flow chart showing a process for finding z′ according to anexemplary embodiment.

FIG. 48 is a flow chart showing a process for finding z′ according to anexemplary embodiment.

FIG. 49 shows a process for finger writing using the touch interactivesurface.

FIG. 50 shows a process for showing hover of a foreground object.

FIG. 51 schematically shows a setup of an interactive system accordingto an exemplary embodiment.

FIG. 52 schematically shows a scenario where a user interacts with acontent on a 2D physical screen.

FIG. 53 schematically shows a scenario where a user interacts with acontent on a 2D physical screen via a virtual touch surface.

FIG. 54 schematically shows a scenario where a user interacts with a 3Dcontent presented by a 3D display screen.

FIG. 55 shows a head-mounted 3D display (HMD) system according to anexemplary embodiment.

FIG. 56 shows a scenario where a user interacts with a virtual touchsurface.

FIG. 57 shows a scenario where a user interacts with a virtual 3D objectrendered by the HMD system.

FIG. 58 shows an HMD system according to an exemplary embodiment.

FIG. 59 shows an HMD system according to an exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

Embodiments consistent with the disclosure include an interactive inputsystem and a method for interactive input.

Hereinafter, embodiments consistent with the disclosure will bedescribed with reference to drawings. Wherever possible, the samereference numbers will be used throughout the drawings to refer to thesame or like parts.

FIG. 1 schematically shows an interactive system 100 consistent withembodiments of the disclosure. The interactive system 100 includes asensing device 102 and a computer 104. The sensing device 102 isconfigured to sense the motion of an object and transfer the detectedinformation to the computer 104, via a sensing device driver 106installed on the computer 104. The object may be, for example, a hand ora finger of a user. The detected information may include, for example,the three-dimensional (3D) position, orientation, or moving direction ofthe object, or information about the object's touching on or hoveringover another object, such as a surface. The sensing device driver 106reads the output, i.e., the detected information, of the sensing device102, processes the detected information, and outputs tracking results,such as 3D tracking results. The sensing device driver 106 also controlsthe operation of the sensing device 102.

The computer 104 may include other components, such as a CPU 108 and amemory 110. Other applications, such as application 112, may also beinstalled on the computer 104. The computer 104 is also connected to adisplay 114, which may be used to graphically show the tracking resultsoutput by the sensing device 102.

FIG. 2 is a flow chart showing an exemplary process consistent withembodiments of the disclosure. In the exemplary process shown in FIG. 2,the object being detected by the sensing device 102 is a user's hand.

At 201, the user places the sensing device 102 at a certain location.For example, the sensing device 102 may be placed on a table top andface up. The sensing device 102 may alternatively be mounted on thecomputer 104 or on the top of the display 114.

At 202, after the sensing device 102 is placed, the interactive system100 begins the environment calibration process. In some embodiments, inthe environment calibration process, the interactive system 100 detectsbackground environment information, and calibrates a touch interactivesurface. More details about the touch interactive surface will bedescribed later in this disclosure. The environment calibration processmay be fully automated to detect certain known environment objects, suchas, for example, the display 114, a keyboard, or an optically markedtouch pad. Alternatively, the environment calibration process may bemanual. For example, the user may define an environment object as thetouch interactive surface, or define a virtual plane, i.e., an imaginaryplane not on any actual environment object, as the touch interactivesurface. If the environment calibration process is manual, instructionsmay be displayed on, for example, the display 114, or may be deliveredto the user in an audio format through, for example, a speaker (notshown).

At 203, during a normal usage period, the interactive system 100continuously detects a foreground object, such as the user's hand orfinger, and recognizes the foreground object's 3D structure andassociated 3D movement. The interactive system 100 also detects changesin the background environment and recalibrates the background whenneeded.

At 204, the sensing device driver 106 translates the detectedinformation into “3D interaction events” and sends the events toapplications installed on and the operating system (OS) of the computer104. For example, a 3D interaction event may be a 3D position, a 3Dorientation, a size (such as length or width), and fine details of theforeground object, e.g., the user's hand or finger. The applications andthe OS may change state according to the received events, and may updatea graphical user interface (GUI) displayed on the display 114accordingly.

At 205, the sensing device driver 106 compares the detected 3D positionof the foreground object with the touch interactive surface, anddetermines object-to-surface information such as, for example, adistance between the foreground object and the surface, a projectedtwo-dimensional (2D) position of the foreground on the surface. Thesensing device driver 106 then converts the object-to-surfaceinformation to touch events, multi-touch events, or mouse events (206).

At 207, the sensing device driver 106 delivers the events to theapplications or the OS, and translates the touch events into a handwriting process. Since the interactive system 100 can detect theforeground object's distance to and projected position on the touchinteractive surface, before the foreground object actually touches thetouch interactive surface, the interactive system 100 can predict atouch before the touch actually occurs, e.g., when the touch will occurand where on the touch interactive surface the touch will occur. Theinteractive system 100 can also determine and display a “hovering”feedback on the display 114.

At 208, the sensing device driver 106 compares the position of theforeground object with positions of the environment objects, such aspositions of keys of a keyboard. The interactive system 100 may generatehovering feedback about which key the user will press before the useractually presses the key. In some embodiments, the interactive system100 may display a virtual keyboard and such hovering feedback in a GUIon the display 114.

Consistent with embodiments of the disclosure, the sensing device 102may be a stand-alone device separated from the computer 104 but can becoupled to the computer 104 via a wired connection (such as a USB cable)or a wireless connection (such as Bluetooth or WiFi). In someembodiments, the sensing device 102 may be integrated into the computer104, i.e., may be part of the computer 104.

Consistent with embodiments of the disclosure, the sensing device 102may include multiple imaging sensors, such as cameras. The imagingsensors may be visible light imaging sensors which are more responsiveto visible light, or infrared (IR) imaging sensors which are moreresponsive to IR light. The sensing device 102 may also include one ormore illumination sources, which provide illumination in variouswavelengths according to the type of the imaging sensors. Theillumination sources may be, for example, light-emitting diodes (LED's)or lasers equipped with diffusers. In some embodiments, the illuminationsources may be omitted and the imaging sensors detects the environmentallight reflected by an object or the light emitted by an object.

FIGS. 3A and 3B schematically show an exemplary sensing device 300consistent with embodiments of the disclosure. The sensing device 300includes a housing 302, multiple imaging sensors 304, and one or moreillumination sources 306. The imaging sensors 304 and the one or moreillumination sources 306 are all formed in or on the housing 302. Such adesign is also referred to as a uni-body design in this disclosure.

The sensing device 300 shown in FIG. 3A has one (1) illumination source306, while the sensing device 300 shown in FIG. 3B has six (6)illumination sources 306. In the example shown in FIG. 3A, theillumination source 306 is arranged between the imaging sensors 304,while in the example shown in FIG. 3B, the illumination sources 306 areevenly distributed on the housing 302 to provide better illuminationresults such as, for example, a wider coverage or a more uniformillumination. For example, as shown in FIG. 3B, two illumination sources306 are located between the two imaging sensors 304, two illuminationsources 306 are located on the left half of the housing 302, and twoillumination sources 306 are located on the right half of the housing302.

In the figures of the disclosure, LED's are illustrated as theillumination sources, as examples. As discussed above, other lightsources, such as lasers equipped with diffusers, may also be employed.

In some embodiments, illumination within the IR bandwidth is needed.Such an illumination may be invisible to naked human eyes. In suchembodiments, the illumination sources 306 may include, for example,LED's emitting IR light. Alternatively, the illumination sources 306 mayinclude LED's emitting light with broader bands that may encompassvisible light. In such situation, the illumination sources 306 may eachbe accompanied with an IR transmissive filter (not shown) placed, forexample, in front of the corresponding illumination source 306.

In some embodiments, the sensing device 300 may also include an IRtransmissive filter (not shown) placed in front of the imaging sensors304 to filter out visible light. In some embodiments, the sensing device300 may also include lens (not shown) placed in front of the imagingsensors 304 for focusing light. The IR transmissive filter may be placedin front of the lens, or between the lens and the imaging sensors 304.

Consistent with embodiments of the disclosure, the sensing device 300may also include a controlling electronic circuit (not shown). Thecontrolling electronic circuit may control the operation parameters ofthe imaging sensors 304, such as, for example, shutter duration or gain.The controlling electronic circuit may also control the synchronizationbetween or among the multiple imaging sensors 304. Moreover, thecontrolling electronic circuit may control the illumination brightnessof the illumination sources 306, the on/off or duration of theillumination from the illumination sources 306, or the synchronizationbetween the illumination sources 306 and the imaging sensors 304. Thecontrolling electronic circuit may also perform other functions such as,for example, power management, image data acquiring and processing,output of data to other devices, such as the computer 104, or receipt ofcommands from other devices, such as the computer 104.

In some embodiments, the sensing device 300 may further include one ormore buttons configured to turn on/off or reset the sensing device 300,or to force recalibration of the environment. For example, one buttonmay be configured to allow the user to forcibly start the manualcalibration process to calibrate the touch interactive surface.

In some embodiments, the sensing device 300 may also include one or moreindicator lights showing the state of the sensing device 300 such as,for example, whether the sensing device 300 is on or off, is performingthe environment calibration, or is performing the touch interactivesurface calibration.

In the examples shown in FIGS. 3A and 3B, the sensing device 300 isformed as a uni-body in the housing 302. The distance between theimaging sensors 304 is fixed. However, such a distance may beadjustable. FIGS. 4A-4C show an exemplary sensing device 400 which has auni-body design but has movable imaging sensors 304. The distancebetween the imaging sensors 304 may be adjusted via a certain mechanism.For example, in the sensing device 400, the imaging sensors 304 areformed on a guide 404, which is configured to allow the imaging sensors304 to move thereon, so that the distance between the imaging sensors304 may be adjusted. Such a design is also referred to as adjustableuni-body design.

FIGS. 4A-4C show different states of the imaging sensors 304 in whichthe distance between the imaging sensors 304 is different. Forsimplicity, other components, such as the illumination sources, are notshown in FIGS. 4A-4C.

In some embodiments, the sensing device 102 may have multiple separatedunits each having one imaging sensor. Hereinafter, such a design is alsoreferred to as a separate design. FIG. 5 shows an exemplary sensingdevice 500 having a separate design, consistent with embodiments of thedisclosure. The sensing device 500 includes two sensing units 502 and504, each having one imaging sensor 304 and one or more illuminationsources 306. In the example shown in FIG. 5, the sensing unit 502 hasone illumination source 304, while sensing unit 504 has two illuminationsources 306. The sensing units 502 and 504 may each have a controllingcircuit for controlling the operation of corresponding sensing unit.

The sensing units 502 and 504 may each include one or more connectionports 510, either wired or wireless, for connecting to other sensingunits or directly to the computer 104. FIGS. 6A and 6B schematicallyshow two difference schemes for connecting the sensing units 502 and 504to the computer 104. FIG. 6A shows a parallel connection where thesensing units 502 and 504 are directly connected to the computer 104.FIG. 6B shows a serial connection where the sensing unit 502 isconnected to the sensing unit 504, and the sensing unit 504 is furtherconnected to the computer 104. In the set up shown in FIG. 6A, bothsensing units 502 and 504 are controlled by the computer 104 andsynchronized. In the set up shown in FIG. 6B, the synchronization may beforwarded from the sensing unit 504 to the sensing unit 502 so that bothsensing units 502 and 504 are synchronized.

FIGS. 7A and 7B schematically show exemplary arrangements of sensingunits relative to a display 114. Three sensing units 702 are shown ineach of FIGS. 7A and 7B.

Consistent with embodiments of the present disclosure, to detect,recognize, and track a foreground object, such as a hand or a finger ofa user, the brightness of the background may need to be lowered. Thatis, a dark background may need to be created.

In some embodiments, the dark background may be created using polarizedlight. According to these embodiments, a background surface may becoated with a reflective material that has a “non-depolarizing”property, such as shown in FIG. 8A. Reflected light from such a materialmay preserve the circular polarization property of incoming light. Sucha material may be, for example, silver colored. In some embodiments,other color dyes or particles may be mixed with the reflective materialto create desired color, texture, or patterns, such as shown in FIG. 8B.In some embodiments, as shown in FIGS. 8A and 8B, another coating may beformed between the background surface and the non-depolarizing materialcoating.

FIG. 9 shows a sensing device 900 consistent with embodiments of thepresent disclosure, where a first polarizer 902 having a firstpolarization direction is placed in front of the illumination source 306and a second polarizer 906 having a second polarization direction isplaced in front of each of the imaging sensors 304. The first and secondpolarization directions may be inconsistent with each other. The firstand second polarizers 902 and 906 may be circular polarizers.

The light emitted by the illumination source 306 is polarized by thefirst polarizer 902 to have the first polarization direction. When thispolarized light is reflected by the non-depolarizing material coatedover the background surface, the polarization direction is preserved.Since the second polarizers 906 have a polarization directioninconsistent with that of the first circular polarizer 902, thereflected light with un-changed polarization direction, the reflectedlight, or at least most part of the reflected light, cannot pass throughthe circular polarizers 906 to reach the imaging sensors 304. In effect,the background surface appears to be dark or black to the imagingsensors 304.

On the other hand, when the polarized light is reflected by theforeground object, e.g., the hand or finger of the user, the polarizedlight will be de-polarized. Such de-polarized reflected light can passthrough the second polarizers 906 and be received by the imaging sensors304. That is, the foreground objects appears to be bright to the imagingsensors 304, and thus the imaging sensors 304 can “see” the foregroundobjects.

Another method consistent with embodiments of the disclosure forcreating a dark background is to use “invisible” markers. Such“invisible” markers may be invisible to naked human eyes but can bedetected by the imaging sensors consistent with embodiments of thedisclosure. FIGS. 10A and 10B show a background surface 1002 withmarkers 1004. An image of the background 1002 captured by an imagingsensor will show the markers 1004, as shown in FIG. 10A. On the otherhand, a human user will only see a normal, uniform surface withoutmarkers, as shown in FIG. 10B.

A method consistent with embodiments of the present disclosure forcreating a background surface having “invisible” markers will bedescribed in regard to FIGS. 11A and 11B. The method involves the use oftwo types of inks, i.e., a first ink and a second ink, which both appearto naked human eyes as a certain color, such as, for example, black.However, the first ink absorbs, or at least absorbs most of, IR light,while the second ink does not absorb but may reflect IR light.Therefore, the first ink appears to an IR imaging sensor as, forexample, black, while the second ink appears to the IR imaging sensoras, for example, white.

Consistent with embodiments of the disclosure, a first pattern isprinted on the background surface, e.g., a fabric, using the first ink.The first pattern may, for example, be a pattern shown in FIG. 11A,where the dark portion represents the part covered by the first ink. Insome embodiments, the first pattern may be printed using a laserprinter, since the toner of a laser printer is based on carbonparticles, which absorbs IR light. Then a second pattern is printed onthe same background surface using the second ink. The second patternmay, for example, be a pattern shown in FIG. 11B, where the dark portionrepresents the part covered by the second ink. In some embodiments, thesecond pattern may be printed using an ink-jet printer, since the blackink used in an ink-jet printer is based on non-IR-absorbing black dyes.In some embodiments, both the first and second patterns may be printedusing copperplate printing.

In some embodiments, the first pattern and the second pattern areessentially reversed to each other. That is, where a point in the firstpattern is dark, the corresponding point in the second pattern isbright. As a result, the background surface exhibits a uniform colorwithout patterns to naked human eyes, such as the background surface1002 shown in FIG. 10B. On the other hand, the imaging sensors candetect the pattern on the background surface, such as that shown in FIG.10A.

In some embodiments, the printing described above may also be a singlephase printing process using one inkjet printer which contains two typesof inks, i.e., a carbon based ink and a non-carbon based ink.

The methods for using the interactive system 100 and related algorithmsconsistent with embodiments of the disclosure will be described below.In some embodiments, the imaging sensors 304 may be calibrated beforeuse. If the sensing device 102 employs a uni-body design, such as thatshown in FIG. 3A or 3B, the calibration of the imaging sensors 304 maybe performed during the manufacturing process of the sensing device 102.On the other hand, if the sensing device 102 employs an adjustableuni-body design, such as that shown in FIG. 4A, 4B, or 4C, or a separatedesign, such as that shown in FIG. 5, the user may customize theposition of each imaging sensor 304. In such situation, the calibrationof the imaging sensors 304 may be performed each time the placement ofthe sensing device 102 is changed.

FIG. 12 is a high level process flow schematically showing a sensingprocess consistent with embodiments of the disclosure. At 1202, theenvironment is calibrated, sensor parameters are adjusted, andbackground is analyzed and recorded. At 1204, foreground object trackingis performed. Foreground objects, e.g., hands or fingers of the user,are continuously detected, and the detected information is output to thecomputer 104, for example, output to applications installed on thecomputer 104. At 1206, the interactive system 100 continuously monitorswhether there is a need to re-calibrate the environment during theforeground object tracking. Alternatively, the user may manually forceto re-start the calibration process.

Consistent with embodiments of the disclosure, the calibration processmay generate multi-sensor calibration data that may be used for, e.g.,removing distortion in an image output from an imaging sensor due to,e.g., imperfect lens. This may make the computer vision calculation andimage processing easier and more accurate. The multi-sensor calibrationdata may also be used for calculating the 3D position of an object or apoint using the pixel position of the object or the point in the imageoutput from the imaging sensor.

In some embodiments, a static calibration may be performed before theinteractive system 100 is used. The static calibration uses achecker-board and allows the imaging sensors 304 to take synchronizedimages when the user moves the checker-board to differentlocations/orientations. The interactive system 100 analyzes the capturedimages and generates camera calibration data including, for exampleintrinsic information of the imaging sensors 304, distortion of theimaging sensors 304, and rectification of multiple imaging sensors 304.

In some embodiments, an automatic calibration may be used during the useof the interactive system 100. The automatic calibration does not need achecker-board and does not need a dedicated calibration session beforeusing the interactive system 100. The automatic calibration is suitablewhen the user frequently changes relative positions of the imagingsensors 304 in, e.g., a separate design or an adjustable uni-bodydesign, or when the user adds customized lenses or customized imagingsensors 304 into the interactive system 100. According to the automaticcalibration, when the user starts to use the interactive system 100, theimaging sensors 304 each take a synchronized snap shot. The interactivesystem 100 finds matching features, e.g., a finger tip, between snapshots taken by different imaging sensors, and records paired pixelcoordinates of the same feature, e.g., the same finger tip, that appearsin different snap shots. This process is repeated to collect a set ofpaired pixel coordinates, and the set of paired pixel coordinates areused by an imaging sensor calibration algorithm consistent withembodiments of the disclosure.

FIG. 13 shows a process consistent with embodiments of the disclosurefor adjusting the illumination sources 306 and the imaging sensors 304,and estimating the background.

At 1302, the imaging sensors 304 capture videos or images of abackground.

At 1304, the brightness of environment light is observed. Theillumination intensity of the illumination sources 306 is adjustedaccording to the observed environmental brightness. In some embodiments,the illumination intensity is adjusted to be low enough to save energybut high enough to distinguish the foreground objects, e.g., hands orfingers, from the background.

At 1306, the gain level and the shutter duration of the imaging sensorsare adjusted so that the final image is bright enough. Higher gain levelresults in brighter but nosier images. Longer shutter duration resultsin brighter images, but the images may be blurry when the foregroundobject is moving. In some embodiments, 1302 and 1304 are performed in aloop to find optimal illumination intensity of the illumination sources306 and parameters of the imaging sensors 304.

At 1308, a background model is analyzed and estimated. At 1310, thebackground model is recorded. When tracking a foreground object, newimages will be compared to this background model to distinguish theforeground object from the background.

FIG. 14 schematically shows a process consistent with embodiments of thedisclosure for analyzing and recording the background model. Thisprocess may be performed for each of the imaging sensors 304. As shownin FIG. 14, at 1402, a number of images are captured and accumulated.The number of accumulated images may be a pre-set fixed number, such as,for example, 100. Alternatively, the number of accumulated images may bevariable, depending on when the background model analysis converges.

At 1404, the background model is analyzed based on the accumulatedimages. In some embodiments, the background model may include, forexample, an average brightness and a maximum brightness of each pixel, abrightness variance, i.e., noisiness, of each pixel, or a local textureproperty and local color property of each pixel.

At 1406, the background model is stored, and the process ends.

FIG. 15 schematically shows a process for recognizing and tracking aforeground object, e.g., a hand or a finger, based on multiple (2 ormore) imaging sensors 304. For each imaging sensor 304, an image iscaptured (1502). The captured image is compared to the stored backgroundmodel to obtain a foreground image (1504). At 1506, the foreground imageis analyzed and the object's 2D structure is obtained.

Then, at 1508, the analyzing results from each imaging sensor 304 arecombined and processed to obtain the foreground object's 3D structure.

FIG. 16 schematically shows a process consistent with embodiments of thedisclosure for finding the foreground object and recognizing theforeground object's 2D structure for each imaging sensor 304. In theexample shown in FIG. 16 and related figures, the scenario that theforeground object is the user's hand is discussed.

At 1602, the background model previously obtained is loaded. Thebackground model may be, for example, a brightness-based backgroundmodel, where the maximum brightness of each pixel for, e.g., 100 initialframes is stored. FIG. 17 shows an exemplary background model image.

Referring again to FIG. 16, a loop is performed to capture new imagesand analyze the 2D structure of the foreground object. In someembodiments, at 1604, a new 2D input image is captured by an imagingsensor 304. FIG. 18 shows an exemplary input image captured during ahand tracking process.

Referring again to FIG. 16, after the input image is obtained, thefollowing is performed: 1) find the foreground object (1606), 2) analyzesub-structures of the foreground object (1608 and 1610), and 3) analyzedetailed properties of the foreground object (1612 and 1614). Details ofsuch a process is described below.

At 1606, the new input image from the imaging sensor 304 is comparedwith the background model to extract a foreground region. In thebackground model, each pixel at position (x,y) may have a feature vectorB(x,y). For example, if the background model is based onintensity/brightness, then B is a scalar, and the value of B(x,y) is thebrightness of the pixel at position (x,y). If the background model isbased on noisiness, then B is a scalar, and the value of B(x,y) is thevariance at position (x,y). In some embodiments, for the new inputimage, the feature vector for every pixel, In(x,y), is calculated.Similar to B(x,y), the value of In(x,y) may be brightness or variancedepending on what background model is used. A difference between In(x,y)and B(x,y) is calculated for each pixel position. If the difference at apixel position is greater than a certain threshold, that pixel isdetermined to belong to the foreground region. Otherwise, that pixel isdetermined to belong to the background.

FIG. 19 shows an exemplary foreground region, in which white pixelsrepresent the foreground object.

Referring again to FIG. 16, at 1608, within the foreground region, ateach pixel position (x,y), the pixel's probability of being part of afinger tip, P_tip(x,y), the pixel's probability of being part of afinger trunk, P_finger(x,y), and the pixel's probability of being partof a palm P_palm(x,y) are calculated.

In some embodiments, the probabilities P_tip(x,y), P_finger(x,y), andP_palm(x,y) may be calculated by comparing a brightness distribution ina neighbor region around the pixel position (x,y) with a set ofpre-defined templates, such as a finger tip template, a finger trunktemplate, and a palm template. The probability of a pixel being part ofa finger tip, a finger trunk, or a palm, i.e., P_tip(x,y),P_finger(x,y), or P_palm(x,y) may be defined by how well the neighborregion fits the respective template, i.e., the finger tip template, thefinger trunk template, or the palm template.

In some embodiments, the probabilities P_tip(x,y), P_finger(x,y), andP_palm(x,y) may be calculated by performing a function/operator F on theneighbor region of a pixel position (x,y). The function/operator fitsthe brightness of the neighbor region with light reflection model of afinger or a finger tip, and return a high value if the distribution isclose to the reflection of a finger trunk (reflection from a cylindershape), or a finger tip (reflection from a half dome shape).

FIG. 20 shows an exemplary result of the above-discussed probabilitiescalculation. In FIG. 20, a region having black and white mosaic has ahigh probability of being a finger tip, a region having vertical hatchlines has a high probability of being a finger trunk, and the whiteregion is a region likely to be a palm, for example.

Referring again to FIG. 16, at 1610, the calculated probabilitiesP_tip(x,y), P_finger(x,y), and P_palm(x,y) are used to segment theforeground object, e.g., the user's hand, into fingers and palm. FIG. 21shows a result of the segmentation. In FIG. 21, the regions with shadowsare the fingers and the white region is the palm.

The probabilities P_tip(x,y), P_finger(x,y), and P_palm(x,y), and thesegmentation results may be used to calculate a hand structure,including finger skeleton information. As used in this disclosure, afinger skeleton refers to an abstraction of the structure of a finger.In some embodiments, the finger skeleton information may include, forexample, a center line (also referred to as a skeleton line) of thefinger, a position of the finger tip, and a boundary of the finger.

In some embodiments, after the user's hand is segmented to the fingersand the palm, the 2D boundary of a sub-part of the hand, e.g., a fingeror a palm, may be obtained. FIG. 22 schematically shows the 2Dboundaries of the sub-parts of the hand. As discussed above, theboundary of a finger may be part of the finger skeleton information.

Referring again to FIG. 16, at 1612, a finger's center line iscalculated by finding and connecting center positions on scanning linesacross the finger. As used herein, a scanning line refers to a linealong which the process for finding the center position is performed.The scanning line may be, for example, a horizontal line. In someembodiments, for a scanning line L(y) in a finger, a weighted average ofthe position x of every pixel (x,y) on the horizontal line L(y) iscalculated using the probability P_finger(x,y) as a weighting factor.This weighted average of the position x is the center position,x_center=C(y), on the scanning line L(y).

After all the scanning lines in the finger are processed, a series ofcenter positions C(y) on the scanning lines L(y) is obtained. Connectingthese center positions provides the center line of the finger, i.e., thefinger skeleton's center line. FIG. 23 schematically shows the centerlines for the fingers.

Referring again to FIG. 16, also at 1612, a finger tip's position,(Tx,Ty) is calculated. The finger tip's position may be defined as theposition of a top region of the finger that matches the shape and shadeof a finger tip. In some embodiments, the finger tip's position may becalculated by averaging the positions of all pixels in the finger tipusing the probability P_tip(x,y) as a weighting factor. For example,

$\begin{matrix}{{Ty} = \frac{\sum\limits_{y}{\sum\limits_{x}{{P\_ tip}\left( {x,y} \right)*y}}}{\sum\limits_{y}{\sum\limits_{x}{{P\_ tip}\left( {x,y} \right)}}}} & (1)\end{matrix}$

In other embodiments, the finger tip's position may be calculated byusing the probability P_finger(x,y) as a weighting factor to average thepositions of the pixels in the top region of the finger. In theresulting finger tip position (Tx,Ty), such as, for example, the resultshown in FIG. 24, both Tx and Ty are float point numbers, having asub-pixel resolution.

FIG. 25 is a high-level flow chart showing a process for calculating 3Dinformation of the foreground object and sub-parts of the foregroundobject consistent with embodiments of the disclosure. Similar to theprocess shown in FIG. 16, in FIG. 25, the user's hand is used as anexample of the foreground object.

At 2502, the 2D sub-structure results, e.g., fingers or palm, fromdifferent imaging sensors 304 are compared and an association betweensub-parts of the foreground object observed by different imaging sensors304 is created. For example, finger A observed by imaging sensor A maybe associated with finger C observed by imaging sensor B. In someembodiments, the association may be based on minimizing the total fingertip distance between all finger pairs, such as shown in FIG. 26. In theexample shown in FIG. 26, the left half and the right half respectivelyshow a 2D image of a hand, i.e., the foreground object, captured by twodifferent imaging sensors 304.

Referring again to FIG. 25, at 2504, features, such as 2D finger tip, 2Dskeleton line, and 2D boundary points, of associated sub-parts arefurther associated, to obtain finger tip pairs, skeleton line pairs, andboundary point pairs, respectively. FIG. 27 schematically shows anexample of associating a first 2D skeleton line of a finger in a first2D image (upper left image) taken by a first imaging sensor 304 and asecond 2D skeleton line of the finger in a second 2D image (upper rightimage) taken by a second imaging sensor 304. As a result of theassociation, a skeleton line pair image (bottom image) is obtained.

Referring again to FIG. 25, at 2506, 2508, and 2510, 3D skeleton line,3D finger tip, and 3D boundary points (e.g., 3D shape of the hand,finger, or palm) are calculated, respectively, as described in moredetails below.

At 2506, a finger tip pair, T1(Tx1,Ty1) and T2(Tx2,Ty1), is processed toobtain 3D information, such as 3D position T(Tx,Ty,Tz), of thecorresponding finger tip. In some embodiments, a 3D reprojectionfunction may be used to calculate the 3D tip position T(Tx,Ty,Tz). The3D reprojection function may use the 2D positions (Tx1,Ty1) and(Tx2,Ty1) of the finger tip, and information of the imaging sensors 304and the lenses, such as, for example, focal length, sensor's pitch(e.g., pixels per millimeter), separation between the two imagingsensors 304 (baseline). In some embodiments, a disparity, d=Tx1−Tx2, iscalculated and used as an input for the 3D reprojection function. Theoutput of the 3D reprojection function is the 3D position (Tx,Ty,Tz) ofthe finger tip. The 3D position (Tx,Ty,Tz) may have a physical unit, andthus may also be expressed as (fx,fy,fz).

In some embodiments, the 3D reprojection function may be expressed usinga 4×4 perspective transformation matrix obtained during the imagingsensor calibration process. This matrix may be a disparity-to-depthmapping matrix.

At 2508, using the skeleton line pair obtained as described above, a 3Dskeleton line for the corresponding finger is calculated. In someembodiments, for the skeleton line pair, pixels on the two 2D skeletonlines are paired based on their y direction to obtain pairs of pixels. Apair of pixels may be processed in a manner similar to that describedabove for the processing of finger tip pairs, to obtain a 3D position ofa point corresponding to the pair of pixels, as shown in FIG. 28. Afterall pairs of pixels are processed, the resulting points are connected toobtain the 3D skeleton line, as shown in FIG. 28.

Referring back to FIG. 25, at 2510, 3D positions of boundary points for,e.g., fingers or palms, are calculated based on 2D positions of theboundary points on the images taken by two different imaging sensors304. In some embodiments, the 3D position of a boundary point may becalculated in a manner similar to that for calculating the 3D positionof the finger tip. After the 3D positions of the boundary points arecalculated, the corresponding points in the 3D space may be connected toobtain the 3D boundary.

FIG. 29 shows the calculation of a 3D boundary of a palm based on 2Dboundaries of the palm in two 2D images taken by two different imagingsensors 304.

The above-obtained information may be combined to generate an output,such as the exemplary output shown in FIG. 30, which shows the 3D tips(the circles in FIG. 30) of the fingers, the 3D skeleton lines (thelines in FIG. 30) of the fingers, and the 3D shape of the hand.

For some applications such as painting and sculpturing, the user mayneed to use a finger or a pen as a tool. In such situation, the fingeror the pen may need to be abstracted as a cylinder shape, and itsdirection and length may need to be calculated. Referring again to FIG.25, at 2512, the direction and length of a finger is calculated.

In some embodiments, the finger is abstracted as a cylinder shape andits length is defined as the length of the cylinder shape, which mayalso be referred to as a finger cylinder length. The finger cylinderlength may be defined as a distance between a very top point of theskeleton line of the finger or the position of the finger tip,P0(x,y,z), and a stop point P1(x,y,z). In some embodiments, the stoppoint P1 is the end of the skeleton line or the point where the skeletonline deviates from a straight line, e.g., where a difference from theskeleton line and a straight line is greater than a threshold.Similarly, the direction of the finger may be defined as the directionof a line connecting points P1 and P0.

At 2514, the 3D position and the orientation of the palm are calculated.The 3D position of the palm may also be referred to as a 3D center ofthe palm, which may be obtained by, for example, averaging the 3Dpositions of the boundary points shown in FIG. 29. FIG. 31 schematicallyshows the calculated 3D center of the palm.

The size and the orientation of the palm may be obtained by comparingthe 3D center of the palm, 3D positions of the boundary points of thepalm, 3D positions of the finger tips, and the directions of thefingers.

The embodiments discussed above are based on direct matching of multipleviews (images) taken by different imaging sensors 304. Embodimentsdiscussed below are related to a model based framework. The model basedframework may improve the hand recognition reliability. For example, themodel based framework may work for a single imaging sensor 304. That is,the 3D recognition of a hand may still be realized even if only a singleimaging sensor 304 is used, because the brightness and the width of afinger from a single image may be used to derive a 3D finger positionestimation. Moreover, with the model based framework, when a hand or afinger is partially visible in one view, but fully visible in anotherview, the interactive system 100 may reliably produce 3D hand trackingresults. Even when a finger is obstructed, e.g., the finger mergingtogether with another finger or bending into the palm region, and thusbecoming invisible in all views, the position of that finger may stillbe continuously predicted.

Consistent with embodiments of the disclosure, when the foregroundobject can only be viewed by a single imaging sensor 304, the distancefrom the foreground object to the imaging sensor 304 may be estimatedbased on the brightness of the foreground object or the size of theforeground object. Then, such a distance may be combined with theposition, i.e., 2D coordinates, of the foreground object in the view ofthe imaging sensor 304 to calculate a 3D position (x,y,z) of theforeground object.

Assuming other parameters, e.g., intensity of the illumination light andreflectance of the foreground object, are the same, the brightness ofthe foreground object, B, is inversely proportional to the square of thedistance from the object to the illumination light. In some embodiments,since the illumination light is close to the imaging sensor 304, thedistance from the object to the illumination light is approximatelyequal to the distance from the object to the imaging sensor 304, i.e.,D_(obj-sensor). This relationship can be expressed using the followingequation:

$\begin{matrix}{B = {\frac{1}{D_{{obj}\text{-}{sensor}}^{2}} \times K}} & (2)\end{matrix}$

In the above equation, coefficient K incorporates the effect of otherparameters such as the intensity of the illumination light and thereflectance of the foreground object, and may be a constant. The aboveequation can be rewritten as:

$\begin{matrix}{D_{{obj}\text{-}{sensor}} = \sqrt{\frac{K}{B}}} & (3)\end{matrix}$

Coefficient K can be calculated while the foreground object is able tobe viewed by two or more imaging sensors 304. In such a situation, asdiscussed above, the 3D position of the foreground object can becalculated and thus the distance D_(obj-sensor) can be obtained. Thedistance D_(obj-sensor) may be continuously monitored to recordD_(obj-sensor) at time t: D_(obj-sensor)(t). Meanwhile, the brightnessof the foreground object at time t, B(t), can be obtained from imagescaptured by the two or more imaging sensors 304. PluggingD_(obj-sensor)(t) and B(t) into Eq. (2) or Eq. (3) above, coefficient Kcan be calculated.

Then, if at time t′, only one single imaging sensor 304 can detect theforeground object, the brightness of the foreground object at t′, i.e.,B(t′), and the coefficient K can be plugged into Eq. (3) to calculateD_(obj-sensor)(t′).

Similarly, the size of the foreground object in an image captured by animaging sensor 304 may also be used to estimate D_(obj-sensor). The sizeof the foreground object in an image captured by an imaging sensor 304can be expressed as follows:

$\begin{matrix}{L = {\frac{1}{D_{{obj}\text{-}{sensor}}} \times K^{\prime}}} & (4)\end{matrix}$

where coefficient K′ incorporates the effect of other parameters, suchas the actual size of the foreground object. Eq. (4) can be rewrittenas:

$\begin{matrix}{D_{{obj}\text{-}{sensor}} = {\frac{1}{L} \times K^{\prime}}} & (5)\end{matrix}$

Similar to the embodiments where the brightness of the foreground objectis used to estimate D_(obj-sensor), in the embodiments of using the sizeof the foreground object in the image captured by the imaging sensor 304to estimate D_(obj-sensor), coefficient K′ can be calculated while theforeground object is able to be viewed by two or more imaging sensors304, when the distance D_(obj-sensor) may be continuously calculated andmonitored to record D_(obj-sensor) at time t: D_(obj-sensor)(t).Meanwhile, the size of the foreground object in the image captured bythe imaging sensors 304 at time t, L(t), can be obtained from thecaptured images. Plugging D_(obj-sensor)(t) and L(t) into Eq. (5) or Eq.(6) above, coefficient K′ can be calculated.

Then, if at time t′, only one single imaging sensor 304 can detect theforeground object, the size of the foreground object in the capturedimage at t′, i.e., L(t′), and the coefficient K′ can be plugged into Eq.(5) to calculate D_(obj-sensor)(t′).

In some embodiments, the above-described methods for estimatingD_(obj-sensor) may be combined to provide a more accurate result. Thatis, an estimate D_(obj-sensor) _(_) ₁ and an estimate D_(obj-sensor)_(_) ₂ are obtained based on the brightness and the size, respectively.Then, a sensor fusion method, such as, for example, a sensor fusionusing extended Kalman filter, is used to combine D_(obj-sensor) _(_) ₁and D_(obj-sensor) _(_) ₂ to obtain D_(obj-sensor).

Consistent with embodiments of the disclosure, the model based frameworkmay be suitable for any number of views, either one view or two or moreviews. FIG. 32 shows a scenario of two views. The details of the modelbased framework according to some embodiments is described below.

For each view, a 2D hand structure analysis (described in previousframework) is performed. The 2D hand structure analysis produces a 2Dhand structure (also referred to as a new 2D hand structure), includinga 2D hand skeleton. Similar to the finger skeleton, a hand skeletonrefers to an abstraction of the structure of a hand.

Tracking is then applied by combining the last 2D hand structure(obtained during the last update) and the new 2D hand structure(obtained during the current update as described above). The trackingprocess includes: 1) apply a filter on previous results to “predict” apredicted 2D hand structure; 2) use the association method to combinethe new 2D hand structure with the predicted 2D hand structure; and 3)update the filter using the combined new result. This tracking processcould produce a smooth skeleton position, is resistant to a sudden lossof finger in a view, and could provide a consistent finger ID. As usedin this disclosure, a finger ID refers to an ID assigned to a detectedfinger. Once a finger is assigned a finger ID, even if it becomesinvisible in following updates, that finger will still carry the samefinger ID. For example, in one update, a middle finger and an indexfinger are detected. The middle finger is assigned a finger ID“finger#1” and the index finger is assigned a finger ID “finger#2”. Theycarry the assigned finger ID's throughout the process, even when one orboth of them become invisible during later updates.

In some embodiments, filtering is applied on a 3D hand model to producea smooth 3D result, including a 3D hand skeleton, which is re-projectedto create a projected 2D hand skeleton on each view.

Then, for each view, the new 2D hand skeleton and the projected 2D handskeleton are combined to obtain an association between finger IDs.

Then, 2D results of both views are combined to calculate a new 3Dposition of the hand and a new 3D finger skeleton. The final result isused as a new 3D hand model, which may be used in the next update.

As described above, the interactive system 100 may be used to recognizeand track the 3D position and orientation, etc. of a foreground object(such as a hand or a finger). Using this feature, a user may interactivewith the computer 104. For example, the user may click and move a fingeron a surface of a desk or a table to control the cursor movement andclick on the display 114, as if the user is using a mouse, without theuse of an actual mouse, so as to use such a surface as a physical touchsurface. With the interactive system 100, the user may also use thescreen of the display 114 as if it is a touch screen, even if the screenof the display 114 is not an actual touch screen. Moreover, the user mayspecify a virtual surface in an open space (such as in the air) as avirtual touch surface, i.e., an imaginary touch surface. By moving thefinger relative to the virtual touch surface, the user may interact withthe computer 104 as if there is an actual touch surface at the positionof the virtual touch surface. In addition, by combining with eyeposition tracking (detection of 3D positions of the user's eyes using,for example, head tracking technology), a direct correlation between theuser's perceived finger position and the position on the screen of thedisplay 114 may be created. Hereinafter, such an interaction is alsoreferred to as a 2.5D touch interaction, and the surface, either aphysical touch surface, a virtual touch surface, or a display screen,mentioned above for realizing the interaction is also referred to as atouch interactive surface. Consistent with embodiments of thedisclosure, a 2.5D touch interaction may include information such as,for example, the 2D projected position of a foreground object, such as afinger tip, on the touch interactive surface, the distance between theforeground object, such as a finger tip, and the touch interactivesurface, and the 3D direction of a foreground object, such as a finger,relative to the normal direction of the touch interactive surface.

FIGS. 33A and 33B schematically show exemplary setups of the system anddifferent types of touch interactive surfaces. In the example shown inFIG. 33A, the sensing device 102 is positioned above the table, such as,for example, above the display 114, and faces down. In some embodiments,the sensing device 102 may be clipped to the top of the display 114. Forexample, the sensing device 102 may be clipped at the center, the left,or the right of the top of the display 114. In some embodiments, thesensing device 102 may be placed on a stand-alone support, which holdsthe sensing device 102 above the table. In the example shown in FIG.33B, the sensing device 102 is placed on the table and faces up. Besidesinteracting with the computer 104 via the interaction with a touchinteractive surface, the user may also interact with the computer 104via the interaction in the 3D interactive space shown in FIGS. 33A and33B. Such an interaction may also be referred to as a 3D interaction.

Consistent with embodiments of the disclosure, the 2.5D touchinteraction may be realized based on 3D information of a foregroundobject obtained as described above and by adding a hovering state of theforeground object to a standard touch interaction. The 2.5D touchinteraction consistent with embodiments of the disclosure may providethe projected (x,y) position of the foreground object, such as, forexample, a finger, on the touch interactive surface, as well as adistance between the foreground object and the touch interactivesurface.

FIG. 34 is a high-level flow chart showing a process consistent withembodiments of the disclosure for enabling a 2.5D touch interactionusing, for example, a hand. At 3402, the environment is defined toprovide environment information, including automatically or manuallydefining a touch interactive surface in the environment. At 3404, 3Dhand tracking is performed, to obtain 3D information of finger tipsaccording to methods described earlier in this disclosure. At 3406, the3D information is converted to 2.5D touch information. At 3408, it isdetermined whether calibration needs to be reset. If so, the processproceeds to 3402. If the calibration does not need to be reset, theprocess proceeds to 3410, where it is determined whether the calibrationneeds to be refined. If so, the process proceeds to 3412 to refine thecalibration. If the calibration does not need to be refined, the processproceeds to 3404. In some embodiments, when surface changes aredetected, the calibration may be reset or refined automatically. In someembodiments, the user may manually force to reset or refine thecalibration.

FIG. 35 is a high-level flow chart showing a process consistent withembodiments of the disclosure for manually calibrating a touchinteractive surface. At 3502, the interactive system 100 instructs theuser how to manually calibrate a touch interactive surface. Theinstructions may be delivered, for example, via a GUI displayed on thescreen of the display 114 or via an audio device, such as a speaker. Theinstructions instruct the user to move a finger to a certain position ona surface and hold steady for a certain period of time. The 3D positionof the user's finger or finger tip is then detected (3504) and recorded(3506). Then the process returns to 3502 to instruct the user to movethe finger to another position on the surface. The process is repeateduntil the calibration process is finished. The recorded 3D positions ofall calibration touch points are then used to define the touchinteractive surface.

In some embodiments, three calibration touch points may be enough todefine the touch interactive surface. In some embodiments, four or moretouch points may be used to define the touch interactive surface. Usingfour or more touch points may increase the accuracy when the user triesto define a physical surface as the touch interactive surface. Moreover,using four or more touch points may also allow the user to define anon-planar surface as the touch interactive surface.

Since the defined touch interactive surface may be large, theinteractive system 100 also allows the user to define an effectiveinteraction area, which may then be mapped to the size of the screen ofthe display 114. This process is shown in FIG. 36. At 3602, theenvironment calibration data, including the 3D positions of thecalibration touch points, is input and analyzed to find top-left (TL),top-right (TR), bottom-left (BL), and bottom-right (BR) points, asschematically shown in FIG. 37. At 3604, an area center and a plane sizeare calculated to obtain a size of the touch interactive surface and acenter position of the touch interactive surface.

Consistent with embodiments of the disclosure, the touch interactivesurface may be automatically and progressively detected by detecting theaction of the user's finger hitting a surface. That is, the interactivesystem 100 detects events of the user's finger tapping a hard surfaceand automatically registers these tapping events. The interactive system100 stores the 3D position of the finger tip in atouch-surface-calibration database when a tapping event occurs. In someembodiments, the interactive system 100 may dynamically repeat thecalibration process to enhance the understanding of the surfaces in theenvironment. Using this method, the user may simply tap on a surface formultiple times at different places and the interactive system 100 wouldautomatically calibrate the surface. Therefore, the interactive system100 does not need to show instructions to guide the user, and the userdoes not need to wait for the interactive system 100 to tell him when toput the finger on the surface or when to move to another place on thesurface. Moreover, after the calibration phase, when the user is usingthe input device as normal, the interactive system 100 continues tomonitor tapping events and update the surface calibration when needed.Therefore, recognition of the touch interactive surface becomes more andmore accurate during the user's continuous use. Moreover, when theenvironment has changed (e.g., the existing surface is removed, or a newsurface is placed), the interactive system 100 automatically updates thetouch interactive surface, by merging new tapping events with existingdatabase.

Below, a method for detecting a tapping event is described. Consistentwith embodiments of the disclosure, 3D position of the user's finger istracked and a time-dependent position value is recorded. To detect atapping event, the time-dependent position value is converted to a speedvalue by differentiation. FIGS. 38A and 38B show a finger's 3D velocitywhen the finger is moving in the air and when the finger hits a solidsurface, respectively. In FIGS. 38A and 38B, only the velocity componentin the y direction is shown. The velocity components in the x and zdirections may also be depicted in a similar manner.

In some embodiments, a moving window is used to detect the followingconditions: 1) the speed drops from a high value (higher than a firstspeed threshold) to a very small value (lower than a second speedthreshold close to zero) within a very short period of time (shorterthan a first time threshold), and 2) the speed keeps at the very smallvalue for a time period longer than a certain period of time (longerthan a second time threshold). If both conditions are satisfied, then itis determined that a tapping event has occurred.

When the user's finger hits a hard surface, sometimes the finger maycontinue to slide on the surface instead of coming to a full stop. Insuch situation, a tapping event is determined as having occurred if thefollowing two conditions are satisfied: 1) a sudden change of fingerspeed in the original traveling direction is detected, and 2) thefollowing movement of the finger is constrained in a 2D plane. This canbe calculated by applying a dimension reduction method, e.g., Principalcomponent analysis (PCA), on the 3D position data of the finger in thetime window to map the trajectory from a physical 3D coordinate into anew 3D coordinate. The PCA algorithm produces the new 3D coordinatesystem by analyzing the 3D position data of the finger. The new 3Dcoordinate system is defined by three axes. Every axis in the new 3Dcoordinate system has an eigenvalue, related to the amount of variationof the data points along that axis. Among the three axes, the one havingthe smallest eigenvalue is referred to as a “minimum axis.” If the speedvalue in the minimum axis keeps very low (lower than a certain speedthreshold) for a relatively long period of time (longer than a certaintime threshold), then the time at which the sudden change of fingerspeed occurs is registered as a time at which a tapping event occurs.

When a new tapping event is detected, the position at which the newtapping occurs (referred to as new tapping position) is used to updatethe existing touch sensitive surface. Consistent with embodiments of thedisclosure, if the new tapping position is consistent with the existingtouch interactive surface, the new tapping position is used to increasethe resolution and accuracy of the existing touch interactive surface.If the new tap position conflicts with the existing touch interactivesurface (which may mean that the user has slightly moved the surface),the existing touch interactive surface is updated using the new tappingposition or the existing touch interactive surface is deleted. If thenew tapping position is not associated with the existing touchinteractive surface, a new touch interactive surface is created.

FIG. 39 is a flow chart showing a process consistent with embodiments ofthe disclosure for automatically detecting a touch interactive surfaceby detecting markers. The markers may be created using methods describedabove in this disclosure. As shown in FIG. 39, at 3902, a user places apiece of sheet with such markers in the environment, for example, on atable. At 3904, the interactive system 100 takes images of the sheetusing the imaging sensors 304, and recognizes the markers. In someembodiments, the interactive system 100 records 3D positions of themarkers in the images. At 3906, the interactive system 100 calculatesthe 3D position, orientation, and size of the sheet based on the 3Dpositions of the markers. The calculation results are saved as touchinteractive surface calibration data.

FIG. 40 is a flow chart showing a process consistent with embodiments ofthe disclosure for automatically detecting and calibrating a displayscreen, such as the screen of the display 114, and making the displayscreen the touch interactive surface. As shown in FIG. 40, at 4002, theinteractive system 100 displays a 2D code, such as a checker board, onthe display screen, such as shown in FIG. 41. At 4004, the interactivesystem 100 takes images using different imaging sensors 304. At 4006,the interactive system 100 recognize the markers in the 2D code, andrecord the 2D positions of the markers in each image. At 4008, theinteractive system 100 calculates the 3D positions, orientations, andsizes of the markers, and derives and records the size, 3D position, and3D orientation of the display screen. At 4010, the interactive system100 displays the surface position, direction, and size. Later, theinteractive system 100 can detect the user's touch interaction on thedisplay screen.

FIG. 42 is a flow chart showing a process consistent with embodiments ofthe disclosure for defining a virtual touch surface. The virtual touchsurface may be defined over the keyboard and between the user and thedisplay screen, and the user may interact in the air with the virtualtouch surface to control the computer 104. As shown in FIG. 42, at 4202,the interactive system 100 instructs the user to “touch” four cornerpoints of the desired virtual touch surface, as schematically shown inFIG. 43. At 4204, the interactive system 100 detects the 3D position ofthe user's hand. At 4206, the interactive system 100 records thepositions of the four corner points. At 4208, the interactive system 100calculates and record the size, 3D position, and 3D orientation of thevirtual touch surface.

As compared to a physical touch screen on a computer monitor, thevirtual touch surface has certain advantages. For example, for laptopand desktop PC users, the distance to the touch screen is far, and theangle is close to vertical (70 degree˜80 degree). At such distance andangle, the screen is not suitable for touching—hard to reach and easy tocause fatigue. On contrast, the virtual touch surface consistent withembodiments of the disclosure may be defined to be closer to the userand at an angle that is easy to operate.

As discussed above, the interactive system consistent with embodimentsof the disclosure may be used to realize a 2.5D touch interaction.Details of the 2.5D touch interaction are described below.

In some embodiments, the user's hand is used as the foreground object.The interactive system 100 uses the 3D tracking information of the hand(such as, for example, the 3D positions of finger tips and the 3Dcylinder direction and length information of fingers) and theenvironment calibration data to perform a 3D to 2.5D conversion, so asto obtain 2D information such as, for example, a distance from a fingertip to a touch interactive surface defined according to, e.g., methodsdescribed above, and the direction of a finger relative to the normal ofthe touch interactive surface.

FIG. 44 is a flow chart showing an exemplary process consistent withembodiments of the disclosure for converting 3D information of aforeground object, such as, for example, a hand or a finger, to 2.5Dinformation. At 4402, 3D information of the touch interactive surface iscalculated based on the position and direction of the touch interactivesurface. The 3D information of the touch interactive surface mayinclude, for example, center of the touch interactive surface and thedirection of the normal of the touch interactive surface. At 4404, the3D position (x,y,z) of the foreground object is projected to the touchinteractive surface, which includes the calculation of, for example, adistance d from the foreground object to the touch interactive surfaceand a 2D position of the projection point on the touch interactivesurface. The 2D position of the projection point on the touchinteractive surface may be expressed as using coordinates x′ and y′ in a2D coordinate system defined on the touch interactive surface. At 4406,the 2D position (x′,y′) of the projection point on the touch interactivesurface and the size of the touch interactive surface are used to scalethe 2D position (x′,y′) of the projection point on the touch interactivesurface to a 2D position (x″,y″) in a 2D coordinate system defined onthe screen of the display 114. As a result of the above process, the 3Dposition (x,y,z) of the foreground object is converted to a 2D position(x″,y″) on the screen of the display 114 and a distance d between theforeground object and the touch interactive surface.

FIG. 45 is a flow chart showing an exemplary process consistent withembodiments of the disclosure for determining the distance d between theforeground object and the touch interactive surface. As described above,during the environment calibration stage, environment calibration datais recorded, including positions of calibration points for defining thetouch interactive surface, i.e., P1(x1,y1,z1), P2(x2,y2,z2), etc. At4502, such environment calibration data and 3D position of theforeground object (x,y,z) are used to find a point having a position(x′,y′,z′) on the touch interactive surface that is the closest to theforeground object. Position (x′,y′,z′) is then compared with position(x,y,z) to determine the distance d (4504).

FIG. 46 is a flow chart showing a process according to exemplaryembodiments of the disclosure for finding z′. In the example shown inFIG. 46, the touch interactive surface may be approximated using apolynomial surface fitting equation:

a*x+b*y+c*z+d+e*x̂2+f*ŷ2+ . . . =0  (4)

At 4602, the positions of all the calibration points are plugged intothe following error function to find an error value:

err=sum[sqr(a*x+b*y+c*z+d+e*x̂2+f*ŷ2+ . . . )]  (5)

In some embodiments, a regression method is used to find best values forparameters a, b, c, d, e, f . . . that minimize the error value “err”.At 4604, the x, y coordinates of the foreground object (which has a 3Dposition of (x,y,z)) are plugged into the polynomial surface fittingequation to calculate z′ at given x and y.

FIG. 47 is a flow chart showing a process according to exemplaryembodiments of the disclosure for finding z′. In the example shown inFIG. 47, a machine learning method using Gaussian process regression isused. As shown in FIG. 47, at 4702, a covariance matrix is calculatedusing the 3D positions of all calibration points. At 4704, a regressionis used to project the query point, i.e., the foreground object, ontothe touch interactive surface and to obtain z′. The method shown in FIG.47 may be suitable for scenarios where the touch interactive surface isirregular, i.e., the touch interactive surface is not a flat plane ornot close to a flat plane, or where the environment measurement data isnot very uniform.

FIG. 48 is a flow chart showing a process according to exemplaryembodiments of the disclosure for finding z′. In the example shown inFIG. 48, a surface point cloud method is used. At 4802, 3D touchinteractive surface is reconstructed from a point cloud based on theenvironment calibration data. At 4804, surface z′ value at position(x,y) is calculated based on the reconstructed surface.

The 2.5D information obtained according to embodiments consistent withthe disclosure, such as those described above, may be used in variousapplications. For example, FIG. 49 shows a process for finger writingusing the touch interactive surface. At 4902, 3D position of a fingertip is tracked. At 4904, the acquired 3D position (x,y,z) of the fingertip is converted to 2.5D information x′, y′, and d. At 4906, it isdetermined whether d is smaller than a threshold distance. If yes, atouch/drag event is recorded (4908). If d is not smaller than thethreshold distance, the event is released (4910).

FIG. 50 shows a process for showing hover of a foreground object, suchas the user's finger, over a key on a keyboard. At 5002, keys on thekeyboard are recognized and each key's 3D position is detected andrecorded. At 5004, the 3D position of the user's finger is compared withthe positions of the keys to determine over which key the finger ishovering and the distance between the finger and that key. At 5006, a UIis displayed on the screen of the display 114 to show that the finger ishovering on that key and how far the finger is away from that key.

As described above, the interactive system 100 can track the position ofa user's hand or finger. In some embodiments, the interactive system 100also tracks the position of the user's eye, and combine the informationabout the position of the eye and the information about the position ofthe hand or finger for 3D/2D input.

Consistent with embodiments of the disclosure, the interactive system100 can detect the 3D position of the user's eye in a manner similar tothat described above for detecting the 3D position of the user's hand orfinger. The information about the eye, the hand or finger, and thescreen of the display 114 is correlated to create a “3D and 2D directmanipulation” interaction. As used in this disclosure, a “directmanipulation” refers to a manipulation that allows the user to directlymanipulate objects presented to them. From the user's eye's point ofview, the position of the hand or finger is the same as the position ofthe object being manipulated, which is displayed on a screen, e.g., a 2Dposition of an object presented by a conventional display device or a 3Dposition of an object presented by a 3D display.

FIG. 51 schematically shows a setup consistent with embodiments of thedisclosure. As shown in FIG. 51, the sensing device 102 is placed toface the user, and may capture images including both the user's head5102 and the hand 5104.

With the head tracking and the hand tracking combined, the user caninteract with a content on a 2D screen or with a content on a 2D screenvia a virtual touch surface. The user can also interact with a 3Dcontent presented by a 3D display. Moreover, a head mounted 3D display(HMD) may be realized.

FIG. 52 schematically shows a scenario where the user interacts with acontent on a 2D physical screen 5202. In some embodiments, the facerecognition and tracking method is used to recognize the 3D position ofthe eye 5204, E(x,y,z), in the coordinates of the sensing device 102.The hand tracking method, such as one of those described above, is usedto recognize the 3D position of the hand 5104, T(x,y,z), in thecoordinates of the sensing device 102 and the action of the hand 5104.As described above, during the calibration phase, the interactive system100 detects and records 3D information of the screen 5202 in thecoordinates of the sensing device 102. Such information may include, forexample, the 3D position and 3D orientation of the screen 5202, thedimension (e.g., width and height) of the screen 5202. Such informationmay alternatively or additionally include, for example, the 3D positionsof the four corners of the screen 5202: UpperLeft(x,y,z),UpperRight(x,y,z), BottomLeft(x,y,z), and Bottom Right(x,y,z). With the3D positions of the eye 5204 and the hand 5104, E(x,y,z) and T(x,y,z), aline extending from the 3D position of the eye 5204 and the 3D positionof the hand 5104 is created. An intersection point I(x,y,z) of this lineintersecting with the screen 5202 is calculated. The coordinates of theintersection point I(x,y,z) can be translated to the 2D coordinates ofthe screen 5202. As a result, a 2D intersection position P(x″,y″)expressed using the 2D coordinates of the screen 5202 is obtained.Information about the user's action at position P(x″,y″) is sent to theoperating system or the applications.

FIG. 53 schematically shows a scenario where the user interacts with acontent on a 2D physical screen 5202 via a virtual touch surface 5302,such as a virtual touch surface defined according to methods consistentwith embodiments of the disclosure, as described above. The calculationsin this scenario are similar to those in the scenario described withrespect to FIG. 52, except that the 2D intersection position P(x′,y′) ofthe line connecting the eye 5204 and the hand 5104 intersecting with thevirtual touch surface 5302 is calculated and recorded, which isexpressed using the 2D coordinates of the virtual touch surface 5302. Inaddition, the distance D between the hand 5104 and the virtual touchsurface 5302 is calculated and reported to the operating system or theapplications.

FIG. 54 schematically shows a scenario where the user interacts with a3D content presented by a 3D display screen 5402, such as a virtual 3Dobject 5404. In some embodiments, the interactive system 100 uses a facerecognition and tracking algorithm to recognize the 3D position of theeyes, E(x,y,z), in the coordinates of the sensing device 102. The handtracking method, such as one of those described above, is used torecognize the 3D position of the hand 5104, T(x,y,z), in the coordinatesof the sensing device 102 and the action of the hand 5104. During thecalibration phase, the interactive system 100 detects and records 3Dinformation of the screen 5402 in the coordinates of the sensing device102. Such information may include, for example, the 3D position and 3Dorientation of the screen 5402, the dimensions (e.g., width and height)of the screen 5402. The interactive system 100 converts the 3D positionof the eye 5204 from the coordinates of the sensing device 102 tocoordinates used by the screen 5402 to render the virtual 3D object5404, Es(x,y,z), and sends this information to the operating system anda 3D interactive application. The 3D interactive application renders thevirtual 3D object 5404 according to the 3D position Es(x,y,z) of theuser's eye 5204. In addition, the interactive system 100 converts the 3Dposition of the hand 5104 from the coordinates of the sensing device 102to coordinates used by the screen 5402 to render the virtual 3D object5404, Ts(x,y,z), and sends this information to the operating system andthe 3D interactive application. The 3D interactive application uses theTs(x,y,z) information to allow the user to interact with the virtual 3Dobject 5404.

A system consistent with embodiments of the disclosure may also includea head mounted 3D display (HMD), which enables virtual realityinteraction, such as, for example, interaction with a virtual touchsurface, interaction with a virtual 3D object, or virtual Interactionwith a physical 3D object. FIG. 55 shows an HMD system 5500 consistentwith embodiments of the disclosure. The HMD system 5500 includes a pairof HMD glasses 5502 and a sensing device 5504 coupled to the HMD glasses5502. The sensing device 5504 may be mounted on the top, the bottom, theleft, or the right of the HMD glasses 5502. In some embodiments, thesensing device 5504 has a separate body design, and imaging sensors ofthe sensing device 5504 are mounted on different places of the HMDglasses 5502.

With the HMD system 5500, the user may interact with a fixed 2D displayin a manner similar to those described above with respect to thescenario where an HMD is not used.

FIGS. 56 and 57 respectively show the scenario where the user interactswith a virtual touch surface and the scenario where the user interactswith a virtual 3D object rendered by the HMD system 5500. The methodswith respect to these scenarios are similar to those described abovewith, e.g., FIGS. 53 and 54.

FIG. 58 shows an HMD system 5800 with which the user may interact with aphysical object 5802 that may locate at a distance far away from theuser. The HMD system 5800 includes the HMD glasses 5502, the sensingdevice 5504, and a global positioning system (GPS) 5804. In someembodiments, the 3D position of the HMD system 5800 in a worldcoordinate system is detected, for example, by the GPS 5804. The 3Dposition of the user's eye in the word coordinate system, Ew(x,y,z), iscalculated. The sensing device 102 detects the 3D position of the hand5104 in the coordinate system of the sensing device 102, T(x,y,z), whichis then converted by the HMD system 5800 to 3D position in the worldcoordinate system, Tw(x,y,z). A line extending from the user's eye tothe 3D position of the hand is calculated in the world coordinatesystem. An intersection between the line and the physical object 5802(the HMD system 5800 has recorded the 3D position of the physical object5802 in the world coordinate system) is detected, and locationinformation of the interaction is acquired and sent to the operatingsystem or the applications.

FIG. 59 shows an HMD system 5900 with which the user may interact with aphysical object 5902. The HMD system 5900 includes the HMD glasses 5502,the sensing device 5504, and a camera 5904. Consistent with embodimentsof the disclosure, the HMD system 5900 uses the camera 5904 or anotherdevice to detect the physical object 5902 and calculates the 3D positionof the physical object 5902 in the coordinate system of the HMD system5900. The HMD system 5900 also detects the 3D position of the hand 5104,T(x,y,z), and calculates a line extending from the user's eye to thehand 5104, in the coordinate system of the HMD system 5900. The HMDsystem 5900 detects and calculates the 3D position of the intersectionbetween the line and the physical object 5902 in the coordinate systemof the HMD system 5900, P(x,y,z), and calculates a distance D betweenthe 3D position of the hand to the 3D position of the intersection. Theobtained information is sent to the operating system or theapplications.

Other embodiments of the disclosure will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A method for human-machine interaction,comprising: monitoring a movement of an object by a sensor that detectspositions of the object over time; generating a time-dependent velocityof the object based on the movement of the object; detecting a tappingevent of the object tapping on a surface by detecting a sudden change ofthe time-dependent velocity; and determining a position of the object ata time when the tapping event occurs as a tapping position of theobject.
 2. The method of claim 1, wherein detecting the tapping eventincludes: determining whether the time-dependent velocity in a certaindirection drops from a first speed value to a second speed value withina first time threshold, the first speed value being larger than thesecond speed value, and the second speed value being close to zero, anddetermining whether the time-dependent velocity in the certain directionkeeps at about the second speed value for longer than a second timethreshold; and determining the tapping event has occurred if thetime-dependent velocity in the certain direction drops from the firstspeed value to the second speed value within the first period of timeand the time-dependent velocity in the certain direction keeps at aboutthe second speed value for longer than the second time threshold.
 3. Themethod of claim 2, wherein monitoring the movement of the objectincludes: recording a time-dependent position value of the object basedon the detected positions over time; and converting the time-dependentposition value to the time-dependent velocity by differentiation.
 4. Themethod of claim 3, wherein: detecting the positions of the objectincludes recording the positions of the object in a firstthree-dimensional (3D) coordinate system, and determining whether thetime-dependent velocity in the certain direction drops from the firstspeed value to the second speed value within the first time thresholdincludes: mapping the positions of the object from the first 3Dcoordinate system to a second 3D coordinate system using a dimensionreduction method, a minimum axis of the second 3D coordinate systembeing along the certain direction; and determining whether thetime-dependent velocity in the certain direction drops from the firstspeed value to the second speed value based on the positions of theobject in the second 3D coordinate system.
 5. The method of claim 4,wherein: mapping the positions of the object from the first 3Dcoordinate system to the second 3D coordinate system includes mappingthe positions using a principal component analysis method, and theminimum axis has a smallest eigenvalue among axes of the second 3Dcoordinate system, an eigenvalue of an axis of the second 3D coordinatesystem relating to an amount of variation of the positions along theaxis in the second 3D coordinate system.
 6. The method of claim 1,further comprising: determining whether the tapping position is on anexisting touch interactive surface of a human-machine interactionsystem; if the tapping position is on the existing touch interactivesurface, using the tapping position to increase a resolution of theexisting touch interactive surface; if the tapping position is slightlyoff the existing touch interactive surface, updating the existing touchinteractive surface using the tapping position or deleting the existingtouch interactive surface; and if the tapping position is not associatedwith the existing touch interactive surface, initiating a process forcreating a new touch interactive surface.
 7. The method of claim 1,further comprising: determining a plurality of tapping positions of theobject; and creating a touch interactive surface based on the tappingpositions.
 8. The method of claim 7, wherein creating the touchinteractive surface based on the tapping positions includes: pluggingcoordinate values of each of the tapping positions into a polynomialsurface fitting equation containing a plurality of parameters; anddetermining best values for the parameters of the polynomial surfacefitting equation using a regression method.
 9. The method of claim 7,wherein creating the touch interactive surface based on the tappingpositions includes creating the touch interactive surface using a pointcloud method.
 10. The method of claim 7, further comprising: after thetouch interactive surface is determined, continuing to detect positionsof the object by the sensor; and determining a distance from the objectto the touch interactive surface based on a position of the object andthe touch interactive surface.
 11. The method of claim 1, furthercomprising: determining a plurality of tapping positions of the object;calculating a covariance matrix using the tapping positions; after thecovariance matrix is calculated, continuing to monitor the position ofthe object; and determining a distance from the object to a touchinteractive surface of a human-machine interaction system represented bythe tapping positions using a Gaussian regression method.
 12. Anapparatus for human-machine interaction, comprising: a sensing deviceconfigured to monitor a movement of an object by detecting positions ofthe object over time; and a processor configured to: generate atime-dependent velocity of the object based on the movement of theobject; detect a tapping event of the object tapping on a surface bydetecting a sudden change of the time-dependent velocity; and determinea position of the object at a time when the tapping event occurs as atapping position of the object.
 13. The apparatus of claim 12, whereinthe processor is further configured to: determine whether thetime-dependent velocity in a certain direction drops from a first speedvalue to a second speed value within a first time threshold, the firstspeed value being larger than the second speed value, and the secondspeed value being close to zero, and determine whether thetime-dependent velocity in the certain direction keeps at about thesecond speed value for longer than a second time threshold; anddetermine the tapping event has occurred if the time-dependent velocityin the certain direction drops from the first speed value to the secondspeed value within the first period of time and the time-dependentvelocity in the certain direction keeps at about the second speed valuefor longer than the second time threshold.
 14. The apparatus of claim13, wherein the processor is further configured to: record atime-dependent position value of the object based on the detectedpositions over time; and convert the time-dependent position value tothe time-dependent velocity by differentiation.
 15. The apparatus ofclaim 14, wherein the processor is further configured to: record thepositions of the object in a first three-dimensional (3D) coordinatesystem; map the positions of the object from the first 3D coordinatesystem to a second 3D coordinate system using a dimension reductionmethod, a minimum axis of the second 3D coordinate system being alongthe certain direction; and determine whether the time-dependent velocityin the certain direction drops from the first speed value to the secondspeed value based on the positions of the object in the second 3Dcoordinate system.
 16. The apparatus of claim 12, wherein the processoris further configured to: determine whether the tapping position is onan existing touch interactive surface of a human-machine interactionsystem; if the tapping position is on the existing touch interactivesurface, use the tapping position to increase a resolution of theexisting touch interactive surface; if the tapping position is slightlyoff the existing touch interactive surface, update the existing touchinteractive surface using the tapping position or delete the existingtouch interactive surface; and if the tapping position is not associatedwith the existing touch interactive surface, initiate a process forcreating a new touch interactive surface.
 17. The apparatus of claim 12,wherein the processor is further configured to: determine a plurality oftapping positions of the object; and create a touch interactive surfacebased on the tapping positions.
 18. The apparatus of claim 12, whereinthe processor is further configured to: determine a plurality of tappingpositions of the object; calculate a covariance matrix using the tappingpositions; after the covariance matrix is calculated, continue tomonitor the position of the object; and determine a distance from theobject to a touch interactive surface of a human-machine interactionsystem represented by the tapping positions using a Gaussian regressionmethod.
 19. A method for human-machine interaction, comprising:monitoring a movement of an object by detecting positions of the objectover time, each position of the object being detected by: obtaining atwo-dimensional (2D) image of the object taken from a viewing angle;extracting a 2D skeleton of the object from the 2D image, the 2Dskeleton including a 2D skeleton line representing a section of theobject; calculating a 3D skeleton of the object based on the 2Dskeleton, the 3D skeleton including a 3D skeleton line representing theobject; and determining the position of the object based on the 3Dskeleton of the object; detecting a tapping event of the object tappingon a surface by detecting a sudden change of the time-dependentvelocity; and determining a position of the object at a time when thetapping event occurs as a tapping position of the object.
 20. The methodof claim 19, wherein extracting the 2D skeleton includes: calculatingprobabilities of pixels in the 2D image being part of the section of theobject; locating the section of the object based on the calculatedprobabilities; calculating, for pixels on a same scanning line in thesection, a skeleton point of the scanning line by performing a weightedaveraging on positions of the pixels on the scanning line using thecalculated probabilities of the pixels on the scanning line as weightingfactors; and obtaining the 2D skeleton line by connecting skeletonpoints on different scanning lines.